1. Field of the Invention
The present invention relates to an electronic piano system accompanied with an automatic performance function.
2. Prior Art
The electronic piano accompanied with the automatic performance function (hereinafter, simply referred to as an automatic performance piano) provides a recording mode where performance information given by a performer is to be recorded and an automatic performance mode where an automatic performance is to be carried out by recorded performance information (or performance information supplied from an external device and the like). In the recording mode when the performance played by the performer is to be recorded, it is necessary to measure a string-striking force of a hammer and then convert a measured string-striking force into an electric signal. In order to carry out the above-mentioned measurement, the conventional automatic performance piano provides a key position sensor for detecting a depressed position of each key and a hammer position sensor for detecting a passing position of each hammer. Then, key-depression and key-release events are detected based on an output of the key position sensor, while a key-striking force is detected based on the timing when the hammer passes through certain set position of the hammer position sensor. The key-striking force obtained at a timing when the key-depression is detected is outputted as data indicative of a velocity of MIDI (Musical Instrument Digital Interface) signal.
However, the conventional automatic performance piano must be complicated in its mechanism because it provides two sensors as described above, which raises up the manufacturing cost of the automatic performance piano.
In general, it can be said that the key-depression speed corresponds to the key-striking force. In this case, the time when the key passed through the key position sensor is measured at first. Then, it is possible to presume the key-striking speed from the measurement result by use of a conversion table which is provided in advance. Thus, by using such conversion table, it is possible to omit the hammer position sensor, by which the construction of the piano can be simplified.
However, the key-depression speed is not constant, because the key-depression speed may be varied from key-depression start timing to key-depression end timing due to the performance technique, performer's habit and the like. In addition, the final string-striking speed of the hammer has strong correlation with variation of the key-depression speed. In short, it is not possible to presume the string-striking force with accuracy by merely detecting the key-depression speed at the predetermined fixed position.
Further, there is a so-called "mis-touch" case where the key is slightly depressed by mistake but the performer does not intend to generate the sound. In such case, if there is provided the key position sensor only, there is a problem in that the string-striking event is detected to be occurred by mistake.
Meanwhile, there is another conventional piano which provides both of the key position sensor for detecting the key-depressed position at one detection point and the hammer position sensor for detecting the hammer-passing positions at two detection points. Herein, it is possible to omit the hammer position sensor by providing the key position sensor which detects the key-depressed positions at two detection points. In this case, by use of the time when the key passes between these two detection points of the key position sensor, the string-striking force is presumed.
In the above-mentioned case, a key touch when the performer returns (or releases) the key is slightly varied in accordance with performance or tune modes such as "legato", "staccato" etc. Based on the difference of key touch, a key-returning (or key-releasing) speed is varied, which affects an operation of a damper which covers the string and prevents it from vibrating. In other words, due to the difference of the key touch, the vibration of string is rapidly stopped in staccato (as shown in FIG. 24) or the vibration of string is smoothly stopped in legato (as shown in FIG. 25). Therefore, in order to reproduce the performance with high fidelity, it is necessary to detect the key-returning speed in the manual performance. Then, based on the detection result, it is necessary to control the key-returning speed in the automatic performance.
However, in the automatic performance piano whose key position sensor detects the key-depressed position at one detection point, it is not possible to detect the key-returning speed.
On the other hand, in another automatic performance piano whose key position sensor detects the key-depressed position at two detection points, it is possible to detect the key-returning speed roughly. Such sensor can merely detect the average speed of the depressing key which passes between two detection points, however, the detected speed cannot correspond to the touch variation. In addition, two detection points are fixed at positions where the key-depression/key-release are detected. Therefore, the distance between two detection points should be so large that sufficient resolution in the speed detection cannot be obtained. In this case, most significant value of the key-returning speed is the value to be detected at a timing when the damper starts to prevent the string from vibrating. In contrast, it is impossible to expect the high fidelity of performance by using the average key-returning speed or the key-returning speeds at other timings. In short, it is necessary to detect the key-returning speed with high resolution at the most significant timing.
Further, the conventional piano fixes the detection points, which cannot be arbitrarily selected.